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Abstract:

The invention relates to 1,1-disubstituted cyclohexane derivatives
containing one or more polymerisable groups, and to liquid-crystalline
media comprising at least one compound of the formula I. At least one of
the polymerisable groups is located at the geminally substituted position
of the cyclohexane ring. The compounds are suitable for the stabilisation
of liquid-crystalline phases. Examples of polymer-stabilised blue phases
are indicated.

Claims:

1. Compounds of the formula I ##STR00106## in which X1 denotes
##STR00107## R1 and R2 each, independently of one another,
denote a radical -Sp-P, a halogenated or unsubstituted alkyl radical
having 1 to 15 C atoms, where, in addition, one or more CH2 groups
in these radicals may each be replaced, independently of one another, by
--C≡C--, --CH═CH--, --(CO)O--, --O (CO)--, --(CO)-- or --O-- in
such a way that O atoms are not linked directly to one another, F, Cl,
Br, CN, SCN, NCS or SF5, where R1 denotes a group -Sp-P if m=0
and X1 does not contain a group -Sp-P, R3 independently is
defined like R2 or denotes H, A1, A2 and A3 each,
independently of one another, denote: a) trans-1,4-cyclohexylene or
cyclohexenylene, in which, in addition, one or more non-adjacent CH2
groups may be replaced by --O-- and/or --S-- and in which H may be
substituted by F, b) 1,4-phenylene, in which one or two CH groups may be
replaced by N and in which, in addition, one or more H atoms may be
replaced by Br, Cl, F, CN, methyl, methoxy or a mono- or polyfluorinated
methyl or methoxy group, or c) a radical from the group
bicyclo[1.1.1]-pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl,
spiro[3.3]heptane-2,6-diyl, tetrahydropyran-2,5-diyl,
1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobut-1,3-diyl,
piperidine-1,4-diyl, thiophene-2,5-diyl, selenophene-2,5-diyl,
##STR00108## in which one or more hydrogen atoms may be substituted by
F, CN, SCN, NCS, SF5, CH2F, CHF2, CF3, OCH2F,
OCHF2 or OCF3, one or more double bonds may be replaced by
single bonds, one or more CH groups may be replaced by N, M denotes
--O--, --S--, --CH2--, --CHY-- or --CYY1--, and Y and Y1
denote Cl, F, CN, OCF3 or CF3, Z1, Z2, Z3 or
Z4 each, independently of one another, denote a single bond, --O--,
--CH2--, --O(CO)CH2, --CH2O--, --CH2OCH2--,
--(CO)O--, --CF2O--, --CH2CH2CF2O--, --CF2CF2--,
--CH2CF2--, --CH2CH2--, --(CH2)4--, --CH═CH--,
--CH═CF--, --CF═CF-- or --C≡C--, where asymmetrical bridges
may be oriented to both sides, m denotes 0, 1, 2 or 3, n denotes 0, 1, 2
or 3, q denotes 0, 1, 2 or 3, P denotes a polymerisable group, and Sp
denotes a spacer group or a single bond.

2. Compounds according to claim 1, in which R1 denotes a group
-Sp-P.

3. Compounds according to claim 1, characterised in that P denotes a
radical of the formula CH.sub.2.dbd.CW1--COO--, in which W1 is
H, F, Cl, CN, CF3, phenyl or alkyl having 1 to 5 C atoms.

4. Compounds according to claim 1, characterised in that m=0.

5. Compounds according to claim 1, characterised in that X1 denotes
a group of the formula ##STR00109## in which the radicals are as
defined in claim 1.

6. Compounds according to claim 1, in which the spacer Sp denotes a group
of the formula Sp'-X, in which Sp' denotes alkylene having 1 to 24,
preferably 1 to 12, C atoms, which is optionally mono- or polysubstituted
by F, Cl, Br, I or CN and in which, in addition, one or more non-adjacent
CH2 groups may each be replaced, independently of one another, by
--O--, --S--, --NH--, --NR0--, --SiR00R000--, --CO--,
--(CO)O--, --O(CO)--, --O(CO)O--, --S(CO)--, --(CO)S--,
--NR00--CO--O--, --O--CO--NR00--, --NR00--CO--NR00--,
--CH═CH-- or --C≡C-- in such a way that O and/or S atoms are
not linked directly to one another, and X denotes a single bond, --O--,
--O(CO)--, --(CH2)2--O--, --CH2(CO)O-- or --OCH.sub.2--.

7. Compounds according to claim 1, characterised in that the number of
polymerisable groups is 2, 3 or 4.

8. Process for the preparation of compounds of the formula I according to
claim 1, characterised in that the polymerisable radicals -Sp-P, --P or
parts thereof are linked to a suitable precursor.

9. Liquid-crystalline medium, characterised in that it comprises one or
more compounds of the formula I of claim 1 or a polymerisation product
thereof.

10. Process for the production of an electro-optical device comprising a
liquid-crystalline, polymer-stabilised medium, characterised in that a
liquid-crystalline medium comprising one or more compounds of the formula
I according to claim 1 is polymerised.

11. Use of one or more compounds of the formula I according to claim 1 as
component of a liquid-crystalline medium or for a polymer in a
liquid-crystalline medium.

12. Use of one or more compounds of the formula I according claim 1 for
the stabilisation of the liquid-crystalline phase in a liquid-crystalline
medium or for the stabilisation of the alignment of a liquid-crystalline
medium.

13. Liquid-crystalline medium according to claim 9, characterised in
that, after stabilisation of the blue phase by polymerisation, it has a
blue phase at least in the range from 20 to 25.degree. C.

14. Use of the liquid-crystalline medium according to claim 9 for
electro-optical purposes.

Description:

[0001] The present invention relates to polymerisable 1,1-disubstituted
cyclohexane derivatives of the formula I, to a process for the
preparation thereof, to the use thereof as components in
liquid-crystalline media (LC media), and to electro-optical display
elements which contain these LC media.

[0003] The blue phase is generally observed at the transition from the
nematic to the optically isotropic state. The medium in the
liquid-crystalline blue phase may be blue, as the name suggests, but also
colourless. The aim of efforts to date was to extend the temperature
range of the blue phase from less than one degree to a range which can be
utilised in practice (cf. H. Kikuchi et al., Nature Materials (2002),
1(1), 64-68; Kikuchi, H. et al., Polymeric Materials Science and
Engineering, (2003), 89, 90-91).

[0005] In practice, the polymer-stabilised blue phases described to date
use, as monomers, a monoreactive non-mesogenic monomer together with a
direactive monomer (RM257).

[0006] The publication WO 2008/061606 discloses polymerisable cyclohexane
derivatives which are substituted in the 1,4-position on the cyclohexane
ring. The cyclohexane ring here may be unsubstituted or substituted by
methyl or fluorine groups, for example 2,
2,3,3,5,5,6,6-octafluorocyclohexane-1,4-diyl compounds.

[0007] Polymerisable liquid-crystal materials of the formula

##STR00001##

are disclosed in DE 36 21 581, where Q1 can denote alkyl or alkoxy
having 1-5 C atoms, F, Cl, Br or CN, for example a CN group, R2
denotes a reactive group, Q denotes a C3-18 alkylene, in which
CH2 groups may be replaced by --O--, --(CO)--, --(CO)O--, --O(CO)--,
--CH═N-- or --CH═CH--, and the other radicals describe chains
(R1), rings (A) and bridges (Z) in between.

[0009] The present invention was based on the object of finding suitable
monomers and corresponding polymers for the stabilisation of
liquid-crystalline phases, in particular blue phases. The polymer is
intended to have the following effects on the properties of the
stabilised LC phase: [0010] broad temperature range of the blue phase,
[0011] fast response time of the device, [0012] small clearing-point
difference on polymerisation, [0013] low operating voltage, [0014] small
variation of the operating voltage with temperature, [0015] low
hysteresis of the transmission of a cell on changing the operating
voltage in order to achieve defined grey shades, [0016] low "memory
effect", i.e. a transmission which is little changed after an on/off
switching cycle.

[0017] In addition, monomer materials which have a good voltage holding
ratio (VHR), have high clearing points and are stable to exposure to
light and temperature are required. Furthermore, good solubility in LC
materials or good miscibility with the LC material is necessary in order
to achieve good distribution in the LC host.

[0018] The aim of the present invention is, in particular, to provide
improved reactive polymerisable compounds which are able to stabilise
blue phases and are thus suitable for the preparation of LC materials
having improved properties.

[0019] This object is achieved in accordance with the invention by
compounds of the general formula I.

[0020] The invention thus relates firstly to compounds of the formula I

##STR00002##

in which X1 denotes

##STR00003## [0021] R1 and R2 each, independently of one
another, denote a radical -Sp-P, a halogenated or unsubstituted alkyl
radical having 1 to 15 C atoms, where, in addition, one or more CH2
groups in these radicals may each be replaced, independently of one
another, by --C≡C--, --CH═CH--, --(CO)O--, --O(CO)--, --(CO)--
or --O-- in such a way that O atoms are not linked directly to one
another, [0022] F, Cl, Br, CN, SCN, NCS or SF5, where R1
denotes a group -Sp-P if m=0 and X1 does not contain a group -Sp-P,
[0023] R3 independently is defined like R2 or denotes H,
[0024] A1, A2 and A3 each, independently of one another,
denote: [0025] a) trans-1,4-cyclohexylene or cyclohexenylene, in which,
in addition, one or more non-adjacent CH2 groups may be replaced by
--O-- and/or --S-- and in which H may be substituted by F, [0026] b)
1,4-phenylene, in which one or two CH groups may be replaced by N and in
which, in addition, one or more H atoms may be replaced by Br, Cl, F, CN,
methyl, methoxy or a mono- or polyfluorinated methyl or methoxy group,
[0027] or [0028] c) a radical from the group
bicyclo[1.1.1]pentane-1,3-diyl, bicyclo [2.2.2]octane-1,4-diyl,
spiro[3.3]heptane-2,6-diyl, tetrahydropyran-2,5-diyl,
1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobut-1,3-diyl,
piperidine-1,4-diyl, thiophene-2,5-diyl, selenophene-2,5-diyl,

[0042] The number of polymerisable groups P is therefore one, two, three
or four, preferably two, three or four.

[0043] The polymerisable group P is a group which is suitable for a
polymerisation reaction, such as, for example, free-radical or ionic
chain polymerisation, polyaddition or polycondensation, or for a
polymer-analogous reaction, for example addition or condensation onto a
main polymer chain. Particular preference is given to groups for chain
polymerisation, in particular those containing a C═C double bond or
--C≡C-- triple bond, and groups which are suitable for
polymerisation with ring opening, such as, for example, oxetane or
epoxide groups.

[0047] The monomers according to the invention are suitable, depending on
the number of polymerisable groups per molecule, for the formation of
polymers which are crosslinked to various extents. If they contain only
one polymerisable group, they form polymer chains. They preferably
contain, at least in some cases, two or more polymerisable groups and
serve as crosslinking agents.

[0048] The term "spacer group" (or "spacer"), also referred to as "Sp"
above and below, is known to the person skilled in the art and is
described in the literature, see, for example, M. Baron, Pure Appl. Chem.
2001, 73(5), 888, and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem.
2004, 116, 6340-6368. Unless indicated otherwise, the term "spacer group"
or "spacer" above and below denotes a flexible group which connects a
ring group and the polymerisable group(s) in a polymerisable compound to
one another.

[0049] Preferred spacer groups Sp are selected from the formula Sp'-X, so
that the radical P-Sp- conforms to the formula P-Sp'-X--, where [0050]
Sp' denotes alkylene having 1 to 24, preferably 1 to 12, C atoms, which
is optionally mono- or polysubstituted by F, Cl, Br, I or CN and in
which, in addition, one or more non-adjacent CH2 groups may each be
replaced, independently of one another, by --O--, --S--, --NH--,
--NR0--, --SiR00R000--, --CO--, --(CO)O--, --O(CO)--,
--O(CO)O--, --S(CO)--, --(CO)S--, --NR00--CO--O--,
--O--CO--NR00--, --NR00--CO--NR00--, --CH═CH-- or
--C≡C-- in such a way that O and/or S atoms are not linked directly
to one another, [0051] X denotes --O--, --S--, --CO--, --(CO)O--,
--O(CO)--, --O(CO)O--, --CO--NR00--, --NR00--CO--,
--NR00--CO--NR00--, --OCH2--, --CH2O--,
--(CH2)2--O--, --SCH2--, --CH2S--, --CF2O--,
--OCF2--, --CF2S--, --SCF2--, --CF2CH2--,
--CH2CF2--, --CF2CF2--, --CH═N--, --N═CH--,
--N═N--, --CH═CR0--, --CY2═CY3--,
--C≡C--, --CH═CH--(CO)O--, --O(CO)--CH═CH-- or a single
bond, preferably a single bond, --O--, --O(CO)--,
--(CH2)2--O--, --CH2(CO)O-- or --OCH2--, [0052]
R00 and R000 each, independently of one another, denote H or
alkyl having 1 to 12 C atoms, and [0053] Y2 and Y3 each,
independently of one another, denote H, F, Cl or CN.

[0054] Typical spacer groups Sp' are, for example, --(CH2).sub.p1--,
--(CH2CH2O)p2, --CH2CH2--,
--CH2CH2--S--CH2CH2--,
--CH2CH2--NH--CH2CH2-- or
--(SiR00R000--O).sub.p1--, in which p1 is an integer from 1 to
24, p2 is an integer from 1 to 6, and R00 and R000 have the
meanings indicated above.

[0057] The radical X1 preferably denotes one of the following
radicals:

##STR00007## ##STR00008## ##STR00009## ##STR00010##

[0058] A1 and A2 may adopt different meanings in the formulae if
they occur more than once for m>1. The same applies analogously to the
groups Z1, Z2 and -Sp-P. The groups -Sp-P are preferably
identical to one another.

[0059] The groups R1, R2 and R3 preferably denote,
independently of one another, a group P-Sp-, alkyl, alkoxy having 1-12 C
atoms or an alkenyl radical having 2-12 C atoms.

[0060] The compounds of the formula I preferably have the following
stereochemistry:

##STR00011##

i.e. the group -Sp-P is in the axial arrangement and the radical
R1--[A1-Z1]m-- is in the equatorial arrangement.

[0061] Analogously thereto, the substituent in the radical X1 which
is drawn to the right (ending in --R2 or --R3) is preferably in
the equatorial arrangement and the substituent drawn to the bottom is
preferably in the axial arrangement.

[0062] The compounds of the formula I according to the invention are
preferably those of the formula IA

##STR00012##

in which P, Sp and X1 are as defined for formula I.

[0063] The compounds according to the invention are highly suitable as
polymerisable components in liquid-crystalline media. The polymer enables
the stabilisation of liquid-crystalline phases, in particular blue
phases. Compared with conventional monomers, a significant reduction in
the operating voltages is observed. At the same time, the tendency
towards the formation of hystereses in the transmission (grey values) can
be controlled depending on the (rising or falling) operating voltage.

[0064] The radicals [P-Sp-] can be in any of the proposed positions. At
least two of these radicals are preferably adjacent in the 1,1-position
on one of the cyclohexane rings. In the formula I, at least one group
from R1 and R3 therefore preferably denotes a radical P-Sp-, or
X1 denotes a radical containing two radicals P-Sp- in R2 and
the adjacent group.

[0065] In a preferred embodiment of the invention, the sum of the
variables m+n+q=0, 1 or 2, or m+n=0, 1 or 2 if q is not present.

[0066] In the following formulae and schemes, the radical R on the
acrylate group generally denotes a radical which is defined like W1
in the polymerisable radical P, i.e. H, F, Cl, CN, CF3, phenyl or
alkyl having 1 to 5 C atoms, in particular the radicals H, F, C1 or
CH3. R preferably denotes H or methyl.

[0067] Particularly preferred compounds of the formula I are therefore the
following illustrative compounds:

[0068] The synthesis of the compounds of the formula I according to the
invention is explained below. In particular, the compounds of the formula
I which contain, as preferred polymerisable group, groups of the acrylate
type in which the polymerisable group P generally denotes a radical of
the formula CH2═CW1--COO--, where W1 is as defined
above for formula I, are discussed. These very particularly preferably
include acrylates (CH2═CH--OCO--) and methacrylates
(CH2═C(CH3)--COO--). The synthesis with other polymerisable
end groups is carried out analogously using suitable methods which are
familiar to the person skilled in the art. This means no difficulty in
the preparation since the polymerisable groups are generally the last to
be attached to the molecule.

[0069] The synthesis of the compounds I is carried out, for example,
starting from dicarboxylic acids of type 3 (Scheme 1). These can be
prepared from cyclohexyl ketones 1 by known processes [W. Schmidt, F.
Vogtle, E. Poetsch, Liebigs Ann. 1995, 1319-1326].

##STR00034##

[0070] With these starting materials 3, the group X═CH2--(CO)--O
is specified as part of the spacer Sp.

[0071] Esterification of the compounds 3 using haloalkanols 4 and
subsequent reaction with acrylic acids 6 (R is preferably H or methyl)
enables, for example, groups Sp composed of Sp'-X, where
X=--CH2--COO-- and Sp'=--(CH2).sub.p1--, to be obtained (Scheme
2).

##STR00035##

[0072] The synthesis from Scheme 2 can alternatively be carried out
directly by esterification of the compounds 3 using compounds 8 (Scheme
3).

[0074] Diol compounds of type 9 can be converted into compounds of type I
where Sp=--(CH2)2-- (=compounds 11 in Scheme 5), for example
directly by reaction with, for example, acryloyl chlorides 10 (R is
preferably H or methyl).

##STR00038##

[0075] The diols 9 here are also suitable starting materials for the
preparation of compounds of type I where X=--(CH2)2--O-- as
part of the spacer Sp.

[0076] Esterification using haloalkylcarboxylic acids 12 to give the
compounds 13 and subsequent reaction thereof with acrylic or methacrylic
acid gives compounds I where
Sp=--(CH2)2--O--(CO)--(CH2).sub.p1-- (=compounds 14 in
Scheme 6).

##STR00039##

[0077] Alkylation of the diols 9 using protected bromo-alkanols 15
(PG=protecting group) gives intermediates 16 for compounds I with spacer
groups containing ether functions
(Sp=--(CH2)2--O--(CH2).sub.p1--). These are then
correspondingly deprotected to give the compounds 17 and can then be
converted, for example, into acrylates (R═H, Me are preferred)
(Scheme 7). The latter can either be carried out via DCC esterification
using acrylic acids 6 (Method A) or by reaction with acryloyl chlorides
10 (Method B).

##STR00040##

[0078] Compounds of the type of the formula 18 can also be prepared
starting from the dibromides 19. These compounds are accessible from the
diols 9 by reaction with, for example, hydrogen bromide [L. A.
Karamysheva, T. A. Geivandova, et al. Mol. Cryst. Liq. Cryst. 1983, 99,
169-175]. A reaction can subsequently be carried out with suitable
alcohols 20 to give the intermediates 17 (Scheme 8).

##STR00041##

[0079] The dibromo compounds 19 can also undergo SN reactions with
carbon nucleophiles, for example Grignard reagents 21. In this way, for
example, the particularly preferred compounds containing alkyl spacers
Sp=--(CH2)2--(CH2).sub.p1-- (=compounds 24 in Scheme 9)
can be obtained. The requisite Grignard reagents 21 arise, for example,
from the compounds 15.

##STR00042##

[0080] Further, multifunctionalisable intermediates are the dialdehydes
25. These can be obtained either by reduction of the diacid 3 or by
oxidation of the diols 9 (Scheme 10).

##STR00043##

[0081] A Wittig reaction of the compounds of the formula 25, for example
using reagents of type 26 (PG=protecting group, preferably silyl
protecting group), then enables intermediates to be obtained for the
synthesis of compounds of the formula I containing double bonds in the
spacer group Sp (cf. compounds 29 in Scheme 11).

##STR00044##

[0082] Wittig reagents of type 30 are particularly suitable if compounds
containing alkyl spacers are to be prepared from the dialdehydes 25. The
product of the Wittig reaction is hydrogenated, with the benzyl
protecting group being cleaved off and the double bonds being
hydrogenated. The process is outlined in Scheme 12.

##STR00045##

[0083] In general, the use of protecting groups is not necessary for the
synthesis of the intermediates 28 and 32. Wittig reagents of type 34 can
also be used (Scheme 13).

##STR00046##

[0084] Further preferred reagents for the synthesis of the compounds I
where Sp=--(CH2)--C═C--(CH2).sub.p1-- or
Sp=--(CH2)3(CH2).sub.p1-- are bromoalkyl Wittig salts 35.
The Wittig reaction of the dialdehydes 25 gives the compounds 36, which
can then be reacted, for example, with acrylic acids 6 in the presence of
base to give compounds I where
Sp=--(CH2)--C═C--(CH2).sub.p1-- (cf. compounds 29 in Scheme
14).

##STR00047##

[0085] In order to obtain compounds I where
Sp=--(CH2)3(CH2).sub.p1-- (cf. compounds 33 in Scheme 15)
in this way, the intermediates 36 are hydrogenated. This is followed by
the reaction of the resultant compounds 37 with acrylic acids 6 (Scheme
15).

##STR00048##

[0086] The syntheses depicted in Schemes 1-15 should be regarded as
illustrative. The person skilled in the art will easily be able to apply
the methods described to other starting materials or to vary the end
groups involved. The polymerisable end groups and spacers can be replaced
by other known radicals. The starting materials, reagents and methods
shown can be combined or supplemented in a suitable manner and a
multiplicity of possible compounds of type I can thus be obtained.

[0088] The use of other starting materials 44, 46, 50 and 52, and using
the methods described above, enables further preferred compounds to be
prepared. The compounds 45, 47, 48, 49, 51, 53 and 54 are derived, for
example, from the starting materials 44, 46, 50 and 52 (cf. Scheme 17).
The synthesis of the starting materials 44, 46, 50 and 52 is described
below (cf. Scheme 18).

##STR00052## ##STR00053## ##STR00054##

[0089] The compounds 44, 46, 50 and 52 are synthesised starting from
cyclo-hexylcarboxylic acid esters 55 (cf. Scheme 18). The enolates
obtained by deprotonation using LDA are reacted with CO2. The
resultant compounds 56 are then saponified to give the dicarboxylic acids
44.

[0090] The dicarboxylic acids 44 can then be reduced to the corresponding
diols 46, for example using lithium aluminium hydride as reducing agent.
The dicarboxylic acids 44 can also be starting materials for the
dialdehydes 52 if DIBAL-His used as reducing agent. However, oxidation of
the diols 46, for example via a Swern oxidation, is often more
advantageous. The diols 46 are then also starting materials for the
synthesis of the dibromides 50.

##STR00055##

[0091] Further preferred starting materials for the synthesis of the
compounds I are described in the literature. The synthesis of
tetracarboxylic acids 60 can be carried out starting from dicarboxylic
acid esters 57 [C. R. Davis, D. C. Swenson, D. J. Burton, J. Org. Chem.
1993, 58, 6843-6850].

[0092] The dicarboxylic acid ester 57, the methyl ester is depicted here
by way of example, is deprotonated using LDA, and the enolate of the
compound is reacted with chloroformic acid ester (Scheme 19). An enolate
is then formed from 58 through the use of LiTMP as base. The enolate
formed is in turn reacted with methyl chloroformate with formation of the
compound 59. The latter can then be saponified to give the
tetracarboxylic acid 60.

##STR00056##

[0093] The tetracarboxylic acid 60 can then be used as starting material
for compounds I. This is depicted by way of example in Scheme 20.

##STR00057##

[0094] The synthesis of further intermediates for the synthesis of
compounds I starts from the tetracarboxylic acid ester 59 (Scheme 21,
line 1). In principle, the tetracarboxylic acid 60 is also suitable for
the synthesis of the compounds 62, 63 and 64 (Scheme 21, lines 2-3).
However, the tetracarboxylic acid ester 59 is easier to handle. The
tetraaldehyde 63 and the tetrabromide 64 are derived, for example, from
the tetraol 62.

##STR00058##

[0095] The possible uses of the compounds 62, 63 and 64 are outlined in
Scheme 22.

##STR00059## ##STR00060##

[0096] The reactions depicted in Schemes 18-22 should be regarded as
illustrative. The syntheses can also be applied to starting materials
having more than one ring element (Schemes 23-29).

##STR00061##

##STR00062##

[0097] Particular preference is given to the use of compounds 73-76 in
which Z2-A2 represents a single bond or a 1,4-cyclohexyl
radical. These intermediates can then in turn give compounds of type I
analogously to Scheme 20 and Scheme 22. This is only explained here with
reference to two possible examples (cf. Scheme 25).

##STR00063##

[0098] The synthesis sequences shown above allow the synthesis of
compounds of type I containing two or four identical groups Sp-P. These
compounds are preferred compounds in the sense of the present invention.

[0099] However, compounds containing different groups Sp-P can also be
built up via the carboxylic acid esters 79. This possibility is depicted
by way of example in Scheme 26.

##STR00064## ##STR00065##

[0100] Reaction with DIBAL-H initially only reduces one ester group, for
example, to the aldehyde. Starting from the aldehyde function, the spacer
can be built up by one of the methods described above. This is depicted
by way of example in Scheme 26 for a Wittig reaction with a reagent of
type 35 and subsequent hydrogenation. The remaining ester function in the
compounds 81 can then be converted into another spacer by one of the
methods from Schemes 2-17. A spacer of the same type as above, only with,
for example, a different chain length, or alternatively a completely
different spacer can be selected here. The latter possibility is depicted
by way of example in Scheme 26. Here, a spacer of the type
Sp=--(CO)O--(CH2).sub.q1-- is built up by saponification and
subsequent esterification using a bromo-alkanol 4. Finally, the acrylate
groups are then introduced to give the compounds 85.

[0101] The person skilled in the art will be able to combine the starting
materials, reagents and methods shown in a suitable manner and thus
obtain a multiplicity of possible compounds of type I. At this point, the
synthesis of particularly preferred starting materials 88-102 for
trireactive compounds of the formula I will be depicted.

##STR00066## ##STR00067## ##STR00068## ##STR00069## ##STR00070##

[0102] The following particularly preferred starting materials or
intermediates 103-122 are obtainable in the same or a similar manner.

##STR00071## ##STR00072## ##STR00073##

[0103] Further preferred compounds I are also obtained starting from
cyclohexyl ketones. It is again possible here to introduce different
spacers. As one possibility, the addition of Grignard reagents of type 21
is outlined (Scheme 29).

##STR00074##

[0104] Starting from the compounds 125, the spacers can then be built up
successively, for example using the methods described above. Scheme 30
illustrates this again by way of example with reference to an
esterification using a bromoalkanoic acid 12.

##STR00075##

[0105] Diones are of course also suitable reaction partners for the above
reactions (cf. Scheme 31).

##STR00076##

Compounds of the formula I

##STR00077##

for which m is not equal to 0 and A1 denotes a cyclohexyl or aryl
radical are prepared, for example, as described in Schemes 32 and 33
(compounds 137 and 140). To this end, firstly a cyclohexyl Grignard
reagent (or an aryl Grignard reagent) is added onto cyclohexyl ketones
123. The hydroxyl group, which is preferably in the axial orientation, of
the compounds 136 and 139 is then suitably derivatised.

[0107] The invention thus generally furthermore relates to a process for
the preparation of compounds of the formula I which is characterised in
that the radicals -Sp-P or --P or parts thereof are linked to a suitable
precursor. An acrylic acid derivative is preferably linked to the
suitable precursor. The suitable compound here is generally an alcohol or
a polyol, depending on the number of polymerisable groups. The linking
preferably comprises the formation of an ester or ether. Details on these
reactions can easily be obtained from the above synthesis strategies.

[0108] The invention furthermore relates to the use of the compounds of
the formula I in liquid-crystalline media, in particular the use as
polymerisable component and/or for a polymer in such media. The compounds
are also used for the stabilisation of liquid-crystalline phases, in
particular blue phases. The stabilisation is carried out by
polymerisation in the mixture.

[0109] This type of use is known for other polymerisable compounds and is
described specifically for the case of blue phases in the literature
cited and in the example part. In general, the medium is polymerised at a
temperature at which it is in the blue phase. The stability range of this
phase is thus broadened. The compounds and media according to the
invention are associated with a considerable improvement in the hitherto
achievable properties of the polymer-stabilised media in the blue phase.

[0110] Preferred liquid-crystalline media are characterised in that they
have, after stabilisation of the blue phase by polymerisation, a blue
phase at least in the range from 15 to 30° C., preferably from 10
to 40° C., particularly preferably from 0 to 50° C. and
very particularly preferably from -10 to 60° C.

[0111] The present invention likewise relates to liquid-crystalline media
which comprise at least one unpolymerised monomer of the formula I or
comprise a polymerisation product thereof, i.e. a polymer comprising at
least one monomer component of the formula I, or both. Besides the
compounds of the formula I, the media according to the invention
preferably comprise one or more further compounds which are
liquid-crystalline or mesogenic. Mesogenic in this connection means,
analogously to C. Tschierske et al. in Angew. Chem. 2004, 116, 6340-86 or
M. Baron Pure Appl. Chem. 2001, 73, 845-895, that the compound in
suitable concentrations and at suitable temperatures contributes to the
formation of the desired mesophase. In addition, further mesogenic or
non-mesogenic monomers containing one or two reactive groups, chiral
dopants, stabilisers, assistants or nanoparticles may be present in the
media.

[0112] Particularly preferred media according to the invention are
indicated below: [0113] The medium comprises one or more monoreactive
monomers or a polymer which is built up from one or more monoreactive
monomers and optionally further monomers. The proportion of monoreactive
monomers is preferably 1 to 15%, particularly preferably 2 to 12%. [0114]
Besides the monoreactive monomers mentioned above, the medium comprises
one or more compounds which act as crosslinking agents, which are
distinguished by two or more reactive groups. These may also include the
compounds of the formula I. [0115] The medium comprises one or more
direactive monomers or a polymer which is built up from one or more
direactive monomers and optionally further monomers. The proportion of
direactive monomers is preferably 0 to 9%, particularly preferably 0 to
6%. In a preferred embodiment, all or some of the direactive monomers
belong to the compounds of the formula I according to the invention
containing 2 or more reactive groups. [0116] The sum of mono- and
direactive monomers is preferably 3 to 17%, particularly preferably
6-14%.

[0117] Trireactive or polyreactive (>3) monomers can also be employed.
The trireactive or polyreactive (>3) monomers preferably belong in
some or all cases to the compounds of the formula I.

[0118] The ratio of monoreactive monomers to crosslinking agents is
preferably between 3:1 and 1:1. The ratio is dependent on the number of
reactive groups of the crosslinking agents involved. In the case of the
use of tetrareactive crosslinking agents, it is particularly preferably
between 3:1 and 2:1, and in the case of the use of direactive
crosslinking agents, it is particularly preferably between 1.5:1 and 1:1.

[0119] Monoreactive monomers which differ from compounds of the formula I
have, for example, a structure of the formula

Ra-Sp-P,

[0120] in which P denotes a polymerisable group (cf. above for formula I),
Sp denotes a spacer group or a single bond (cf. above), and Ra
denotes an organic radical having at least 3 C atoms.

[0121] The radical Ra can be a so-called mesogenic radical, which
generally contains one or more rings, or a simple, generally
chain-shaped, non-mesogenic radical.

[0122] Non-mesogenic radicals are preferably straight-chain or branched
alkyl having 1 to 30 C atoms, in which, in addition, one or more
non-adjacent CH2 groups may each be replaced, independently of one
another, by --C(R0)═C(R00)--, --C≡C--,
--N(R00--, --O--, --S--, --CO--, --CO--O--, --O--CO--,
--O--CO--O--in such a way that O and/or S atoms are not linked directly
to one another, and in which, in addition, one or more H atoms may be
replaced by F, Cl, Br, I or CN.

[0123] Preferred meanings of P and Sp correspond to the meanings indicated
below for formula I*.

[0124] Preferred mesogenic monomers containing one, two or more
polymerisable groups which differ from compounds of the formula I are
characterised by the formula I*

Ra--B1--(Zb--B2)m--Rb I*

in which the individual radicals have the following meanings: [0125]
Ra and Rb each, independently of one another, denote P, P-Sp-,
H, halogen, SF5, NO2, a carbon group or a hydrocarbon group,
where at least one of the radicals Ra and Rb denotes or
contains a group P or P-Sp-, [0126] P on each occurrence, identically or
differently, denotes a polymerisable group (cf. above for formula I),
[0127] Sp on each occurrence, identically or differently, denotes a
spacer group or a single bond (cf. above), [0128] B1 and B2
each, independently of one another, denote an aromatic, heteroaromatic,
alicyclic or heterocyclic group, preferably having 4 to 25 ring atoms,
which may also contain fused rings, and which may also be mono- or
polysubstituted by L, [0129] L denotes H, OH, CH2OH, halogen,
SF5, NO2, a carbon group or a hydrocarbon group, [0130] Zb
on each occurrence, identically or differently, denotes --O--, --S--,
--CO--, --CO--O--, --COO--, --O--CO--O--, --OCH2--, --CH2O--,
--SCH2--, --CH2S--, --CF2O--, --OCF2--,
--CF2S--, --SCF2--, --(CH2).sub.n1--,
--CF2CH2--, --CH2CF2--, --(CF2).sub.n1--,
--CH═CH--, --CF═CF--, --C≡C--, --CH═CH--OCO--,
--OCO--CH═CH--, CR0R00 or a single bond, [0131] R0 and
R00 each, independently of one another, denote H or alkyl having 1
to 12 C atoms, [0132] m denotes 0, 1, 2, 3 or 4, [0133] n1 denotes 1, 2,
3 or 4.

[0134] Particularly preferred compounds of the formula I* are those in
which [0135] Ra and Rb each, independently of one another,
denote P, P-Sp-, H, F, Cl, Br, I, --CN, --NO2, --NCO, --NCS, --OCN,
--SCN, SF5 or straight-chain or branched alkyl having 1 to 25 C
atoms, in which, in addition, one or more non-adjacent CH2 groups
may each be replaced, independently of one another, by
--C(R0)═C(R00)--, --C≡C--, --N(R00)--, --O--,
--S--, --CO--, --CO--O--, --O--CO--, --O--CO--O-- in such a way that O
and/or S atoms are not linked directly to one another, and in which, in
addition, one or more H atoms may be replaced by F, Cl, Br, I, CN, P or
P-Sp-, where at least one of the radicals Ra and Rb denotes or
contains a group P or P-Sp-, [0136] B1 and B2 each,
independently of one another, denote 1,4-phenylene, naphthalene-1,4-diyl,
naphthalene-2,6-diyl, phenanthrene-2,7-diyl, anthracene-2,7-diyl,
fluorene-2,7-diyl, coumarine, flavone, where, in addition, one or more CH
groups in these groups may be replaced by N, cyclohexane-1,4-diyl, in
which, in addition, one or more non-adjacent CH2 groups may be
replaced by O and/or S, 1,4-cyclohexenylene,
bicyclo[1.1.1]-pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl,
spiro[3.3]heptane-2,6-diyl, piperidine-1,4-diyl,
decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl,
indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all these
groups may be unsubstituted or mono- or polysubstituted by L, [0137] L
denotes OH, CH2OH, F, Cl, Br, I, --CN, --NO2, --NCO, --NCS,
--OCN, --SCN, --C(═O)N(Rx)2, --C(═O)Y1,
--C(═O)Rx, --N(Rx)2, optionally substituted silyl,
optionally substituted aryl having 6 to 20 C atoms, or straight-chain or
branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy
or alkoxycarbonyloxy having 1 to 25 C atoms, in which, in addition, one
or more H atoms may be replaced by F, Cl, P or P-Sp-, [0138] P and Sp
have the meanings indicated above, [0139] Y1 denotes halogen, [0140]
Rx denotes P, P-Sp-, H, halogen, straight-chain, branched or cyclic
alkyl having 1 to 25 C atoms, in which, in addition, one or more
non-adjacent CH2 groups may be replaced by --O--, --S--, --CO--,
--CO--O--, --O--CO--, --O--CO--O-- in such a way that O and/or S atoms
are not linked directly to one another, and in which, in addition, one or
more H atoms may be replaced by F, Cl, P or P-Sp-, an optionally
substituted aryl or aryloxy group having 6 to 40 C atoms, or an
optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 C
atoms.

[0141] The term "carbon group" denotes a mono- or polyvalent organic group
containing at least one carbon atom, where this either contains no
further atoms (such as, for example, --C≡C--) or optionally
contains one or more further atoms, such as, for example, N, O, S, P, Si,
Se, As, Te or Ge (for example carbonyl, etc.). The term "hydrocarbon
group" denotes a carbon group which additionally contains one or more H
atoms and optionally one or more heteroatoms, such as, for example, N, O,
S, P, Si, Se, As, Te or Ge.

[0142] "Halogen" denotes F, Cl, Br or I, preferably F or Cl.

[0143] A carbon or hydrocarbon group can be a saturated or unsaturated
group. Unsaturated groups are, for example, aryl, alkenyl or alkynyl
groups. A carbon or hydrocarbon group having more than 3 C atoms may be
straight-chain, branched and/or cyclic and may also contain spiro links
or condensed rings.

[0148] Further preferred carbon and hydrocarbon groups are straight-chain,
branched or cyclic alkyl radicals having 1 to 40, preferably 1 to 25, C
atoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br,
I or CN, and in which one or more non-adjacent CH2 groups may each
be replaced, independently of one another, by
--C(Rx)═C(Rx)--, --C≡C--, --N(Rx)--, --O--,
--S--, --CO--, --CO--O--, --O--CO--, --O--CO--O-- in such a way that O
and/or S atoms are not linked directly to one another.

[0149] Rx preferably denotes H, halogen, a straight-chain, branched
or cyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one
or more non-adjacent C atoms may be replaced by --O--, --S--, --CO--,
--CO--O--, --O--CO--, --O--CO--O-- and in which one or more H atoms may
be replaced by fluorine, an optionally substituted aryl or aryloxy group
having 6 to 40 C atoms, or an optionally substituted heteroaryl or
heteroaryloxy group having 2 to 40 C atoms.

[0156] Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e.
they may contain one ring (such as, for example, phenyl) or two or more
rings, which may also be fused (such as, for example, naphthyl) or
covalently linked (such as, for example, biphenyl), or contain a
combination of fused and linked rings. Heteroaryl groups contain one or
more heteroatoms, preferably selected from O, N, S and Se.

[0157] Particular preference is given to mono-, bi- or tricyclic aryl
groups having 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl
groups having 2 to 25 C atoms, which optionally contain fused rings and
are optionally substituted. Preference is furthermore given to 5-, 6- or
7-membered aryl and heteroaryl groups, in which, in addition, one or more
CH groups may be replaced by N, S or O in such a way that O atoms and/or
S atoms are not linked directly to one another.

[0160] The (non-aromatic) alicyclic and heterocyclic groups include both
saturated rings, i.e. those which contain exclusively single bonds, and
also partially unsaturated rings, i.e. those which may also contain
multiple bonds. Heterocyclic rings contain one or more heteroatoms,
preferably selected from Si, O, N, S and Se.

[0161] The (non-aromatic) alicyclic and heterocyclic groups can be
monocyclic, i.e. contain only one ring (such as, for example,
cyclohexane), or polycyclic, i.e. contain a plurality of rings (such as,
for example, decahydronaphthalene or bicyclooctane). Particular
preference is given to saturated groups. Preference is furthermore given
to mono-, bi- or tricyclic groups having 3 to 25 C atoms, which
optionally contain fused rings and are optionally substituted. Preference
is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups, in
which, in addition, one or more C atoms may be replaced by Si and/or one
or more CH groups may be replaced by N and/or one or more non-adjacent
CH2 groups may be replaced by --O-- and/or --S--.

[0163] Preferred substituents are, for example, solubility-promoting
groups, such as alkyl or alkoxy, electron-withdrawing groups, such as
fluorine, nitro or nitrile, or substituents for increasing the glass
transition temperature (Tg) in the polymer, in particular bulky groups,
such as, for example, tert-butyl or optionally substituted aryl groups.

[0164] Preferred substituents, also referred to as "L" above and below,
are, for example, F, Cl, Br, I, --CN, --NO2, --NCO, --NCS, --OCN,
--SCN, --C(═O)N(Rx)2, --C(═O)Y1,
--C(═O)Rx, --N(Rx)2, in which Rx has the meaning
indicated above and Y1 denotes halogen, optionally substituted silyl
or aryl having 6 to 40, preferably 6 to 20, C atoms, and straight-chain
or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl,
alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which
one or more H atoms may optionally be replaced by F or Cl.

[0167] The polymerisable group P is a group which is suitable for a
polymerisation reaction, such as, for example, free-radical or ionic
chain polymerisation, polyaddition or polycondensation, or for a
polymer-analogous reaction, for example addition or condensation onto a
main polymer chain. Particular preference is given to groups for chain
polymerisation, in particular those containing a C═C double bond or
C≡C triple bond, and groups which are suitable for polymerisation
with ring opening, such as, for example, oxetane or epoxide groups.

[0170] The polymerisable compounds and RMs can be prepared analogously to
the process known to the person skilled in the art and described in
standard works of organic chemistry, such as, for example, in
Houben-Weyl, Methoden der organischen Chemie [Methods of Organic
Chemistry], Thieme-Verlag, Stuttgart. Further synthetic methods are given
in the documents cited above and below. In the simplest case, RMs of this
type are synthesised, for example, by esterification or etherification of
2,6-dihydroxynaphthalene or 4,4'-dihydroxybiphenyl using corresponding
acids, acid derivatives or halogenated compounds containing a group P,
such as, for example, (meth)acryloyl chloride or (meth)acrylic acid, in
the presence of a dehydrating reagent, such as, for example, DCC
(dicyclohexylcarbodiimide).

[0171] As a further component, the liquid-crystalline media preferably
comprise non-polymerisable compounds which support the liquid-crystalline
phase, which taken together are also known as host mixture. This
proportion is typically 50 to 95% by weight, preferably 80 to 90% by
weight. In the case of polymer-stabilised blue phases, the
non-polymerisable fraction preferably comprises compounds selected from
Table A (see example part). The fraction preferably consists of 50% by
weight or more of these compounds, very particularly preferably 80% by
weight or more.

[0172] The LC media which can be used in accordance with the invention are
prepared in a manner customary per se, for example by mixing one or more
of the above-mentioned compounds with one or more polymerisable compounds
as defined above and optionally with further liquid-crystalline compounds
and/or additives. In general, the desired amount of the components used
in smaller amount is dissolved in the components making up the principal
constituent, advantageously at elevated temperature. It is also possible
to mix solutions of the components in an organic solvent, for example in
acetone, chloroform or methanol, and to remove the solvent again, for
example by distillation, after thorough mixing. The invention furthermore
relates to the process for the preparation of the LC media according to
the invention.

[0173] It goes without saying to the person skilled in the art that the LC
media according to the invention may also comprise compounds in which,
for example, H, N, O, Cl, F have been replaced by the corresponding
isotopes.

[0174] The present invention furthermore relates to the use of the media
according to the invention in an electro-optical device, preferably a
liquid-crystal display, and to devices of this type. The displays operate
with a polymer-stabilised liquid-crystal phase, which preferably works in
the region of the blue phase or is nematic. The device is preferably
produced by carrying out the polymerisation of the polymerisable
constituents of the medium in the device itself, i.e. in the
opto-electronic cell.

[0175] The invention furthermore relates to the use of polymerisable
compounds according to the invention, and to the use of LC media
according to the invention, in PSA displays (frequently also called PS-VA
displays), in particular to the use in PSA displays containing an LC
medium, for the generation of a tilt angle in the LC medium by in situ
polymerisation of the polymerisable compounds and media according to the
invention in the PSA display, preferably with application of an
electrical or magnetic field.

[0176] For PSA applications, the compounds according to the invention are
preferably combined with the following reactive mesogens as polymerisable
compounds which can easily be polymerised with little or no initiator
under UV light of a suitable wavelength:

##STR00083## ##STR00084## ##STR00085## ##STR00086##

[0177] For the purposes of the present invention, the terms alkyl,
alkenyl, etc., are defined as follows:

[0180] The term "fluoroalkyl" in this application encompasses
straight-chain groups containing at least one fluorine atom, preferably a
terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl,
4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However,
other positions of the fluorine are not excluded.

[0183] Above and below, a 1,4-substituted cyclohexane ring, depicted in
the formulae, with horizontal (=preferably equatorial) and vertical
(=preferably axial) substituents preferably has the following
configuration of the substituents:

##STR00087##

[0184] Some of the substituents drawn here can also denote H.

[0185] Further combinations of the embodiments and variants of the
invention in accordance with the description also arise from the claims.

[0186] In the present application, the term compounds, unless expressly
indicated otherwise, means both one compound and also a plurality of
compounds.

[0187] The following examples are intended to explain the invention
without limiting it. The person skilled in the art will be able to take
procedure details from the examples which are not mentioned specifically
in the general description, generalise these details in accordance with
general expert knowledge and apply them to his specific problem.

[0190] 190.0 g (0.85 mol) of 4'-propylbicyclohexyl-4-one are initially
introduced at 0° C. in 1000 ml (7.0 mol) of methanolic ammonia
solution (7 M), and 273.5 ml (2.6 mol) of ethyl cyanoacetate are added
dropwise. The mixture is left at 5° C. for 3 d, and the resultant
precipitate is filtered off with suction. The filter residue is digested
in diethyl ether and again filtered off with suction. The ammonium salt
obtained in this way is suspended in 3 I of water, and the mixture is
carefully rendered acidic using conc. HCl. The precipitate is filtered
off and washed with cold water. The residue is recrystallised from
ethanol, giving
2,4-dioxo-9-(4-propylcyclohexyl)-3-aza-spiro[5.5]-undecane-1,5-dicarbonit-
rile as a colourless solid.

[0192] A mixture of 50 g (0.14 mol) of
2,4-dioxo-9-(4-propylcyclohexyl)-3-aza-spiro[5.5]undecane-1,5-dicarbonitr-
ile, 800 ml of glacial acetic acid and 1.51 of 60% sulfuric acid is
stirred at 120-125° C. for 5 days. After cooling, the batch is
added to ice-water and extracted a number of times with THF/MTBE (1:1).
The combined organic phases are washed with saturated sodium chloride
solution and dried using sodium sulfate. The solution is concentrated to
dryness, and the residue is recrystallised from acetonitrile/THF (2:1),
giving (4-carboxymethyl-4'-propylbicyclohexyl-4-yl)acetic acid as a beige
solid.

[0194] 10.0 g (0.26 mol) of lithium aluminium hydride are suspended in 200
ml of THF, and a solution of 24.0 g (74.0 mmol) of
(4-carboxymethyl-4'-propylbicyclohexyl-4-yl)acetic acid in 300 ml of THF
is metered in. When the addition is complete, the mixture is stirred at
RT for 1 h and at the reflux temperature for 3 h. The reaction mixture is
hydrolysed using water and neutralised using dil. hydrochloric acid. The
salts are filtered off, and the filtrate is diluted with MTBE. The
solution is washed with saturated sodium chloride solution and dried
using sodium sulfate. The solid remaining after removal of the solvents
is recrystallised from acetonitrile, giving
2-[4-(2-hydroxyethyl)-4'-propylbicyclohexyl-4-yl]ethanol as a beige
solid.

[0196] 18.0 g (60.7 mmol) of
2-[4-(2-hydroxyethyl)-4'-propylbicyclohexyl-4-yl]ethanol are initially
introduced together with 11.6 ml (0.14 mol) of methacrylic acid and 222
mg (1.82 mmol) of DMAP in 160 ml of THF. A solution of 28.0 g (0.14 mol)
of DCC in 40 ml of THF is metered in, and the batch is stirred for 18 h.
4.0 g (31.7 mmol) of oxalic acid dihydrate are added, and the mixture is
filtered. The filtrate is concentrated to dryness, and the residue is
purified by column chromatography (SiO2, dichloromethane). Further
purification is carried out by recrystallisation from isopropanol, giving
2-{4-[2-(2-methylacryloyloxy)ethyl]-4'-propylbicyclohexyl-4-yl}ethyl
2-methacrylate as a colourless solid having a melting point of 37°
C.

[0202] 10.0 g (30.8 mmol) of
(4-carboxymethyl-4'-propylbicyclohexyl-4-yl)acetic acid are heated on a
water separator for 6 h together with 15.0 g (80.4 mmol) of
6-bromo-1-hexanol and 0.50 g (2.90 mmol) of paratoluenesulfonic acid
monohydrate in 150 ml of toluene. After cooling, the reaction mixture is
subjected to absorptive filtration (SiO2, toluene), and the filtrate
is concentrated to dryness. The crude product obtained in this way is
used directly for the next reaction.

[0204] 10.0 g of crude (about 15.4 mmol) 6-bromohexyl
[4-(6-bromohexyloxycarbonylmethyl)-4'-propylbicyclohexyl-4-yl]acetate are
stirred at 50° C. and with exclusion of light for 19 h together
with 7.8 ml (92.7 mmol) of methacrylic acid and 14.9 g (0.11 mol) of
potassium carbonate in 100 ml of DMSO. The suspension is diluted with
MTBE and stirred into water. The organic phase is separated off, and the
aqueous phase is extracted with MTBE. The combined organic phases are
washed with sat. sodium chloride solution. The solution is dried using
sodium sulfate and concentrated to dryness. The crude product is purified
by column chromatography (SiO2, dichloromethane), giving
6-(2-{4-[6-(2-methylacryloyloxy)hexyloxycarbonylmethyl]-4'-propylbicycloh-
exyl-4-yl}acetoxy)hexyl 2-methacrylate as a colourless oil.

[0220] Before the polymerisation of a sample, the phase properties of the
medium are determined in a test cell with a thickness of about 10 microns
and an area of 2×2.5 cm. The cell is filled by capillary action at
a temperature of 75° C. The measurement is carried out under a
polarising microscope with heating stage with a temperature programme of
1° C./min. The polymerisation of the media is carried out by
irradiation with a UV lamp (Dr. Honle, Bluepoint 2.1, 365 nm interference
filter) having an effective power of about 1.5 mW/cm2 for 180
seconds. The polymerisation is carried out directly in the
electro-optical test cell. The polymerisation is carried out initially at
a temperature at which the medium is in the blue phase I (BP-I). The
polymerisation is carried out in a plurality of sub-steps, which
gradually result in complete polymerisation. The temperature range of the
blue phase generally changes during the polymerisation. Between each
sub-step, the temperature is therefore modified so that the medium is
still in the blue phase. In practice, this can be carried out by
observing the sample under the polarising microscope after each
irradiation operation of about 5 s or longer. If the sample becomes
darker, this indicates a transition into the isotropic phase. The
temperature for the next sub-step is reduced correspondingly. The entire
irradiation time which results in maximum stabilisation is typically 180
s at the irradiation power indicated. Further polymerisations can be
carried out in accordance with an optimised irradiation/temperature
programme. Alternatively, the polymerisation can also be carried out in a
single irradiation step, in particular if a broad blue phase is present
even before the polymerisation.

Electro-Optical Characterisation

[0221] After the above-described polymerisation and stabilisation of the
blue phase, the phase width of the blue phase is determined. The
electro-optical characterisation is subsequently carried out at various
temperatures within and if desired also outside this range.

[0222] The test cells used are fitted with interdigital electrodes on the
cell surface on one side. The cell gap, the electrode separation and the
electrode width are typically each 1 to 10 microns. This uniform
dimension is referred to below as the gap width. The area covered by
electrodes is about 0.4 cm2. The test cells do not have an alignment
layer. For the electro-optical characterisation, the cell is located
between crossed polarising filters, with the longitudinal direction of
the electrodes adopting an angle of 45° to the axes of the
polarising filter. The measuring is carried out using a DMS301
(Autronic-Melchers) at right angles to the cell plane. In the
voltage-free state, the arrangement described produces an essentially
dark picture (definition 0% transmission).

[0223] Firstly, the characteristic operating voltages and then the
response times are measured on the test cell. The operating voltage is
applied to the cell electrodes in the form of a rectangular voltage with
alternating sign (frequency 100 Hz) and variable amplitude, as described
below.

[0224] The transmission in the voltage-free state is set as 0%. The
transmission is measured while the operating voltage is increased. The
achievement of the maximum value of about 100% intensity defines the
characteristic quantity of the operating voltage V100. Equally, the
characteristic voltage V10 is determined at 10% of the maximum
transmission. These values are optionally measured at various
temperatures in the range of the blue phase, in any case at room
temperature (20° C.).

[0225] At the lower end of the temperature range of the blue phase,
relatively high characteristic operating voltages V100 are observed.
At the upper end of the temperature range (close to the clearing point),
the value of V100 increases considerably. In the region of the
minimum operating voltage, V100 generally only increases slowly with
temperature. This temperature range, delimited by T1 and T2, is
referred to as the usable, flat temperature range (FR). The width of this
"flat range" (FR) is (T2-T1) and is referred to as the width of
the flat range (WFR). The precise values of T1 and T2 are
determined by the intersections of tangents at the flat curve section FR
and the adjacent steep curve sections in the V100/temperature
diagram. In the second part of the measurement, the response times during
switching on and off (τon, τoff) are determined. The
response time τon is defined by the time taken to achieve 90%
intensity after application of a voltage at the level of V100 at the
selected temperature. The response time τoff is defined by the
time taken to decrease by 90% starting from the maximum intensity at
V100 after the voltage has been reduced to 0 V. The response time is
also determined at various temperatures in the range of the blue phase.
As further characterisation, the transmission for a continuously varied
operating voltage between 0 V and V100 can be measured at a
temperature within FR. Comparison of the curves for increasing and
decreasing operating voltage can give rise to a hysteresis. The
difference between the transmissions at 0.5V100 and the difference
between the voltages at 50% transmission are, for example, characteristic
hysteresis values and are referred to as ΔT50 and
ΔV50 respectively.

[0226] As a further parameter, the ratio of the transmission in the
voltage-free state before and after passing through a switching cycle can
be measured. This transmission ratio is known as the "memory effect". The
value of the memory effect in the ideal state is 1.0. Values above 1 mean
that a certain memory effect is present in the form of excessively high
residual transmission after the cell has been switched on and off. This
value is also determined in the working range of the blue phase (FB).

[0229] M1 and M2 comprise compounds RM-1a/b according to the invention.

[0230] The media are characterised as described before the polymerisation.
The RM components are then polymerised in the blue phase by irradiation
once (180 s), and the media obtained are re-characterised.

[0231] The polymer-stabilised liquid-crystalline media exhibit blue phases
over a broad temperature range. Compared with Comparative Example C2,
lower values are observed for the operating voltage V100 for M1 and
M2 with a comparable memory effect.